> Source: [sk163835](https://support.checkpoint.com/results/sk/sk163835)

# sk163835 - Site-to-Site VPN fails with "no response from peer" error, tcpdump shows source port is a random high port

| Property | Value |
|----------|-------|
| Solution ID | sk163835 |
| Date Created | 2019-12-02 |
| Last Modified | 2026-07-21 |
| Technical Level | Advanced |
| Products | Security Gateway |
| Versions | R82, R81.20, R81.10 (EOS) |
| OS | Gaia |

## Symptoms

- * Site-to-Site VPN fails with error log "*no response from peer*".
* Tcpdumps on the relevant interface shows that the original source port of 500 on IKE traffic is modified to a random high port. No other aspects of the traffic are changed.
* Ike debugs indicate a failure on packet 1 of phase 1.

## Cause

The Gateway is performing a 'HIDE NAT' on the IKE communication.

* Gateway 1 sends packet 1 of phase 1 with a random high source port.
* Gateway 2 responds to the traffic with the same high port, now set as the destination port.
* Gateway 1 receives the traffic, but never processes it as VPN traffic due to the random port.

## Solution

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